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Kunert-Bajraszewska M.,Torun Center for Astronomy | Siemiginowska A.,Harvard - Smithsonian Center for Astrophysics | Labiano A.,CSIC - National Institute of Aerospace Technology
Astrophysical Journal Letters | Year: 2013

We discovered an X-ray cluster in a Chandra observation of the compact steep spectrum (CSS) radio source 1321+045 (z = 0.263). CSS sources are thought to be young radio objects at the beginning of their evolution and can potentially test the cluster heating process. 1321+045 is a relatively low-luminosity source and its morphology consists of two radio lobes on the opposite sides of a radio core with no evidence for jets or hotspots. The optical emission line ratios are consistent with an interstellar medium dominated by active galactic nucleus photoionization with a small contribution from star formation, and no contributions from shocks. Based on these ratios, we classify 1321+045 as a low excitation galaxy (LEG) and suggest that its radioactivity is in a coasting phase. The X-ray emission associated with the radio source is detected with 36.1 ± 8.3 counts, but the origin of this emission is highly uncertain. The current X-ray image of the cluster does not show any signatures of a radio source impact on the cluster medium. Chandra detects the cluster emission at >3σ level out to ∼60″ (240 kpc). We obtain the best-fit beta model parameters of the surface brightness profile of β = 0.58 ± 0.2 and a core radius of 9.4 arcsec. The average temperature of the cluster is equal to keV, with a temperature and cooling profile indicative of a cooling core. We measure the cluster luminosity L (0.5-2 keV) = 3 × 1044 erg s-1 and mass 1.5 × 1014 M⊙. © 2013. The American Astronomical Society. All rights reserved.

Kunert-Bajraszewska M.,Torun Center for Astronomy
Astronomische Nachrichten | Year: 2016

There are numerous examples of radio sources with various sizes which surprisingly exhibit very similar morphology. This observational fact helped to create a standard evolutionary model in which young and small radio-loud active galactic nuclei (AGN), called gigahertz-peaked spectrum (GPS) sources and compact steep spectrum (CSS) sources, become largescale radio objects. However, many details of this evolutionary process are still unclear. We explored evolution scenarios of radio-loud AGN using new radio, optical and X-ray data of so far unstudied low luminosity compact (LLC) sources and we summarize the results in this paper. Our studies show that the evolutionary track is very "individualized" although we can mention common factors affecting it. These are interaction with the ambient medium and AGN power. The second feature affects the production of the radio jets which, if they are weak, are more vulnerable for instabilities and disruption. Thus not all GPS and CSS sources will be able to develop large scale morphologies. Many will fade away being middleaged (105 yr). It seems that only radio strong, high excitation compact AGN can be progenitors of large-scale FRII radio sources. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shulevski A.,University of Groningen | Shulevski A.,Netherlands Institute for Radio Astronomy | Morganti R.,University of Groningen | Morganti R.,Netherlands Institute for Radio Astronomy | And 23 more authors.
Astronomy and Astrophysics | Year: 2015

Context. Steep spectrum radio sources associated with active galactic nuclei (AGN) may contain remnants of past AGN activity episodes. Studying these sources gives us insight into the AGN activity history. Novel instruments like the LOw Frequency ARray (LOFAR) are enabling studies of these fascinating structures to be made at tens to hundreds of MHz with sufficient resolution to analyse their complex morphology. Aims. Our goal is to characterize the integrated and resolved spectral properties of VLSS J1431+1331 and estimate source ages based on synchrotron radio emission models, thus putting constraints on the AGN duty cycle. Methods. Using a broad spectral coverage, we have derived spectral and curvature maps, and used synchrotron ageing models to determine the time elapsed from the last time the source plasma was energized. We used LOFAR, Giant Metrewave Radio Telescope (GMRT) and Jansky Very Large Array (VLA) data. Results. We confirm the morphology and the spectral index values found in previous studies of this object. Based on our ageing analysis, we infer that the AGN that created this source currently has very low levels of activity or that it is switched off. The derived ages for the larger source component range from around 60 to 130 Myr, hinting that the AGN activity decreased or stopped around 60 Myr ago. We observe that the area around the faint radio core located in the larger source component is the youngest, while the overall age of the smaller source component shows it to be the oldest part of the source. Conclusions. Our analysis suggests that VLSS J1431.8+1331 is an intriguing, two-component source. The larger component seems to host a faint radio core, suggesting that the source may be an AGN radio relic. The spectral index we observe from the smaller component is distinctly flatter at lower frequencies than the spectral index of the larger component, suggesting the possibility that the smaller component may be a shocked plasma bubble. From the integrated source spectrum, we deduce that its shape and slope can be used as tracers of the activity history of this type of steep spectrum radio source. We discuss the implications this conclusion has for future studies of radio sources having similar characteristics. © ESO, 2015.

Kunert-Bajraszewska M.,Torun Center for Astronomy | Katarzynski K.,Torun Center for Astronomy | Janiuk A.,Polish Academy of Sciences
Astronomy and Astrophysics | Year: 2015

Aims. We present modelling and interpretation of the continuum broadband emission of two broad absorption line (BAL) quasars. The X-ray weakness of BAL quasars in comparison to non-BAL objects is possibly caused by the absorption of X-ray emission by the shielding material near the equatorial plane. On the other hand, the radio-loud BAL quasars are more X-ray loud than the radio-quiet ones. This suggests that part of the X-ray emission may arise from the radio jet. To investigate this possibility, we modelled the nuclear spectra of two BAL quasars in the whole available energy range. Methods. We focus on the emission from the very centres of these two objects, not greater than several parsecs. The source of emission was approximated by a single, homogeneous component that produces synchrotron and inverse-Compton radiation. The simplicity of the model allowed us to estimate the basic physical parameters of the emitting regions, using a universal analytic approach. Such methods have already been proposed to estimate basic physical parameters in blazars. For the first time, in a simplified form we propose this solution for quasars. In addition, we modelled the radiation spectra of the accretion disk and its corona to compare them with the jets' spectra. Results. We find that in the case of radio and X-ray luminous high-redshift object 3C 270.1, the nuclear X-ray continuum is dominated by the non-thermal, inverse-Compton emission from the innermost parts of the radio jet. However, the radio core of the lobe-dominated PG 1004+130 is probably too weak to produce significant part of the observed X-ray emission. A large contribution from the X-ray emitting accretion disk and corona is produced in our model for a sufficiently high mass of the black hole. However, it then exceeds the observed flux. Because the large intrinsic absorption was postulated recently by the NuSTAR observations, we propose that the disk-corona component may still account for the X-rays produced in this source. This part of the spectrum must nevertheless be dominated by the X-ray jet. The results of our modelling show that the jet-linked X-ray emission is present in both strong and weak radio sources, but its fraction seems to scale with the radio jet power. © 2015 ESO.

Kunert-Bajraszewska M.,Torun Center for Astronomy | Labiano A.,European Space Agency | Labiano A.,Harvard - Smithsonian Center for Astrophysics | Siemiginowska A.,Harvard - Smithsonian Center for Astrophysics | Guainazzi M.,European Space Agency
Monthly Notices of the Royal Astronomical Society | Year: 2014

We report on the first X-ray Chandra observations of a sample of seven low-luminosity compact sources, which belong to a class of young compact steep spectrum (CSS) radio sources. Four of these have been detected, while the other three have upper limit estimations for X-ray flux; one CSS galaxy is associated with an X-ray cluster. We have used the new observations, together with the observational data for known strong CSS and gigahertz-peaked spectrum (GPS) objects and large-scale Fanaroff-Riley types I and II objects (FR I and II), to study the relation between morphology, X-ray properties and excitation modes in radio-loud active galactic nuclei (AGNs). We have found the following. (i) The low-power objects fit well with the already established X-ray-radio luminosity correlation for AGNs and occupy the space among FR I objects, which are weaker in X-rays. (ii) The high-excitation and low-excitation galaxies occupy a distinct locus in the radio/X-ray luminosity plane, notwithstanding their evolutionary stage. This is in agreement with the postulated different origins of the X-ray emission in these two groups of objects. (iii) We have tested the AGN evolution models by comparing the radio/X-ray luminosity ratio with the size of the sources and, indirectly, with their age. We conclude that the division for two different X-ray emission modes, which originate in the base of the relativistic jet (FR Is) or in the accretion disc (FR IIs) is already present among the younger compact AGNs. (iv) Finally, we have found that the CSS sources are less obscured than the more compact GPS objects in X-rays. However, the anticorrelation between X-ray column density and radio size does not hold for the whole sample of GPS and CSS objects. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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